Bacterial vaginosis vs thrush: telling the two apart

Two features separate most cases. The first is smell. BV classically produces a strong fishy odour, which the NHS says is particularly noticeable after sex, while thrush discharge does not usually smell. The second is itch. Thrush typically causes itching, irritation and soreness around the vulva and vagina, whereas the NHS says BV does not usually cause soreness or itching.

Neither feature is perfectly reliable. The NHS says half of women with BV do not have any symptoms at all, and thrush sometimes causes no symptoms either. Because the two conditions need different medicines, and an antifungal will not correct a bacterial imbalance, a swab taken by a clinician is the most dependable way to find out which one you have.

The vagina normally contains a balance of bacteria. In BV that balance changes. The NHS says what causes this is not fully known, but you are more likely to get it if you are sexually active (although it can occur in women who have not had sex), have had a change of partner, have an intrauterine device (IUD) or use perfumed products in or around the vagina. It is not classed as an STI, but sex can trigger it or pass it on, and the NHS says it can be passed between women or anyone with a vagina during sex.

Thrush is a yeast infection. Candida normally lives harmlessly on the body and tends to grow in warm, moist conditions when the balance of bacteria changes. The NHS lists skin that is irritated or damaged, taking antibiotics, poorly controlled diabetes, a weakened immune system, hormone replacement therapy (HRT) and pregnancy among the things that can allow this to happen. Thrush also affects men, and it can occur on other areas of skin.

The table summarises what the NHS says about each condition.

Both NHS pages describe the same approach. A GP or sexual health clinic will ask about your symptoms, may look at the vagina and may wipe a cotton bud over the discharge to test for the cause and for other infections. For BV the NHS specifically says the aim is to confirm it is BV and rule out an STI. For thrush it says the GP wants to confirm it is thrush and rule out other infections.

The NHS adds that sexual health clinics can help with BV, that many offer a walk-in service without an appointment, and that they often get test results quicker than GP surgeries. This is useful to know because the NHS says to see a GP or go to a sexual health clinic if you think you have BV. For thrush, a pharmacist can sell an antifungal if you have had thrush diagnosed before and you know the symptoms, but the NHS says to see a GP the first time you have symptoms.

BV is usually treated with antibiotic tablets, gels or creams prescribed by a GP or sexual health clinic. The NHS says it is common for it to come back, usually within a few months, and that if you get it more than 4 times in a year you may be given an antibiotic gel to put in the vagina for a few months. Thrush usually clears within 7 to 14 days of starting an antifungal. The NHS says you should not use antifungal medicine more than twice in 6 months without speaking to a pharmacist or doctor, and that antifungal creams can damage condoms and diaphragms.

Self-care advice is similar for both. Use water and plain soap, or for thrush water and an emollient, to wash the genital area. Avoid perfumed soaps, bubble bath, shampoo and shower gel, vaginal deodorants, washes and douches, and strong detergents on underwear. For BV the NHS suggests showers instead of baths and not smoking. For thrush it suggests drying properly after washing and wearing cotton underwear rather than tight underwear or tights.

The NHS says BV in pregnancy carries a small chance of complications such as premature birth or miscarriage, although BV causes no problems in the majority of pregnancies, and that it is important to seek treatment if you are pregnant. It advises speaking to a GP or midwife if your vaginal discharge changes during pregnancy. For thrush, it says to see a GP if you are pregnant or breastfeeding.

BV also increases the risk of getting an STI. The NHS suggests this may be because it makes the vagina less acidic and reduces natural defences against infection. This is one reason why a clinician may offer an STI screen when you attend with a change in discharge.

Seek assessment from a GP or sexual health clinic if you have not had either condition diagnosed before, if you are pregnant or breastfeeding, if you are under 16 or over 60 (for thrush), if symptoms return repeatedly, if treatment has not worked or if you have a weakened immune system. A change in discharge that is unusual for you, particularly with pain, bleeding or a fever, deserves a clinical review rather than repeated self-treatment.